Work will continue on the structure and activities of three bacterial ADP-ribosylating exotinins: diptheria toxin, cholera toxin, and exotoxin A from Pseudomonas aeruginosa. Studies of the mechanism of entry of the active fragment of diphtheria toxin into cells will continue. Structure-activity relationships within cholera toxin and exotoxin A will be pursued further, as will the isolation of mutants in the structural gene for cholera toxin. Active site studies on diphtheria toxin and possibly the other two toxins will be initiated. Studies to lay the groundwork for DNA sequencing of the structural gene for diphtheria toxin will continue.